#include <iostream>
#include <string.h>
#include <stdlib.h>
#include <H5Cpp.h>
#include <H5Ppublic.h>
#include <H5Fpublic.h> // for SWMR support
#include <H5File.h>
#include <H5Location.h>

using namespace std;
using namespace H5;

int main (int argc, char* argv[])
{
    FileAccPropList fapl;
    fapl.setLibverBounds(H5F_LIBVER_LATEST, H5F_LIBVER_LATEST);

FYI: add fapl declaration and set LATEST (above) and change this line to the one below
    H5File* _hdf5File = new H5File("/home/here/user/CompressionIssue.h5", H5F_ACC_TRUNC|H5F_ACC_SWMR_WRITE);
    H5File* _hdf5File = new H5File("/home/here/user/CompressionIssue.h5", H5F_ACC_TRUNC|H5F_ACC_SWMR_WRITE, FileCreatPropList::DEFAULT, fapl);

    // Create a scalar data set
    hsize_t dims[1] = {1}; // dataset dimensions at creation
    hsize_t maxdims[1] = {H5S_UNLIMITED}; // dataset maximum potential size
    int rank = 1; // 1 dimensional arrays
    DataSpace dataspace(rank, dims, maxdims);
    DSetCreatPropList* plist = new DSetCreatPropList;
    hsize_t chunkdims[1] = {3600};
    plist->setChunk(rank, chunkdims);
    plist->setDeflate(4); 

FYI: this is for the H5Pset_chunk_opts, there is no C++ wrapper for it, so you
     call the C function directly, passing in the ID returned by getId()

    unsigned opts = 0;
    opts |= H5D_CHUNK_DONT_FILTER_PARTIAL_CHUNKS;
    if (H5Pset_chunk_opts(plist->getId(), opts) < 0)
        throw exception or just exit(0) if you want simple for now

    DataSet ds = _hdf5File->createDataSet("MyScalars", DataType(PredType::NATIVE_DOUBLE), dataspace, *plist);
    delete plist;
    ds.close();

    // write to data set one element at a time - this will be how the data is reported
    DataSpace* filespace = NULL;
    DataSpace* memspace = NULL;
    srand(time(NULL));
    for (int i=0; i<1000; i++) {
        ds = _hdf5File->openDataSet("MyScalars");
        unsigned long npointsToAdd = 1;
        hsize_t npoints = ds.getSpace().getSimpleExtentNpoints();
        if (i==0) npoints--; // replace the first point if this is the initial add to the data set
        // We'll be appending to an existing data set so lets set our "pointer" to the end of the existing data set in the file
        // extend the data - let's add some points to the data set
        hsize_t extend[1] = { npointsToAdd }; // number of points being added
        hsize_t size[1];
        size[0] = npoints + extend[0]; // new size of the data set
        hsize_t offset[1];
        offset[0] = npoints; // where should new value(s) be inserted

        ds.extend(size);
        // Select a "hyperslab" in extended portion of the dataset.
        filespace = new DataSpace(ds.getSpace());
        filespace->selectHyperslab(H5S_SELECT_SET, extend, offset);

        // Define memory space.
        memspace = new DataSpace(1, extend, NULL);
        
        // generate random value and write to file
        double val = (double)rand()/RAND_MAX*1000.0;
        ds.write(&val, DataType(PredType::NATIVE_DOUBLE), *memspace, *filespace);

        // clean up
        delete memspace;
        delete filespace;

        // flush the file
        H5F_scope_t scope = H5F_SCOPE_GLOBAL;
        ds.flush(scope);
FYI: you don't need this line, ds going out of scope takes care of it
        ds.close();
    }

FYI: you don't need this line, delete _hdf5File takes care of it
    _hdf5File->close();

    delete _hdf5File;
  return 0; 
}